With the need for reducing costs or times associated with business trips, more companies are moving towards transmission systems to have teleconference or videoconference among remotely located offices via a communication network. The transmission systems allow transmission of image data or voice data among a plurality of transmission terminals that are remotely located from one another through a communication network such as the Internet to facilitate communication among the plurality of transmission terminals.
The recent transmission systems may be provided with a function of sending notification to one or more transmission terminals that are previously determined when the state of the request transmission terminal changes, for example, as described in Japanese Patent Application Publication No. 2006-295883.